1. Field of the Invention
The present invention relates to an automobile mirror assembly, and more particularly to an electrically operated automobile mirror assembly. More specifically, the present invention pertains to an electrically operated, retractable automobile mirror assembly.
2. Description of the Related Art
In the art of automobile mirrors, such as side mirrors and door mirrors for providing the driver with a rear view, it has been proposed to make the mirrors retractable so that the mirrors are retracted within the contour of the vehicle body or the door assembly when they are not needed. For example, in Japanese utility model application No. 60-149877, which is assigned to the same assignee of the present invention, there is shown an electrically powered automobile mirror assembly which can be retracted by operating the power motor. According to the proposal, the mirror assembly includes, as shown in FIG. 10, a base plate 51 which is secured to a vehicle body 50 and an upright post 52 mounted on the base plate 51. On the post 52, there is rotatably mounted a movable member 53 which carries a rear viewing mirror (not shown). On the movable member 53, there is mounted a power motor 54 which has an output shaft 54a on which a worm 54b is provided. The worm 54b is engaged with an idler gear 55a which is formed integrally with a gear 55. The gear 55 is engaged with a gear 56 which is secured to the post 52. A friction mechanism 57 is provided between the gear 56 and the movable member 53 for preventing a free rotation of the movable member 53. Thus, the movable member 53 is rotated about the post 52 when the motor 54 is energized overcomes the friction force provided by the friction mechanism 57. In order to prevent the mirror assembly from being rotated under an exteral turbulence such as an aerodynamic force to which the mirror is subjected when the vehicle running, it is necessary for the friction mechanism 57 to provide a sufficiently high friction force. It should however be noted that in order to obtain a sufficient friction force, the friction member in the mechanism 57 must be of a large diameter. This is disadvantageous in that the mirror frame dimension must be correspondingly increased. Particularly, in the case where it is required to increase the spacing between the vehicle body 50 and the inner edge 58 of the mirror frame for the purpose of decreasing the aerodynamic force, the increase in the diameter of the friction member is critical. A similar problem is also encountered in the case where the thickness of the mirror frame is to be decreased due to a design requirement. If the diameter of the friction member could be decreased, the axis of the post could be located closer to the vehicle body so that it would be easy to retract the mirror assembly within the outside contour of the vehicle body.
Japanese patent disclosure No. 60-151142 proposes to provide a counter shaft between the motor and the post to provide a further speed reduction gear mechanism. It should however be noted that in this structure the motor must be of a large capacity or of a high performance in order that the motor power can overcome the resistance in the power transmitting gear train. Otherwise, there must be provided a plurality of stages of speed reduction gear mechanisms to thereby decrease the motor capacity. In the case where a plurality of stages of reduction gear mechanisms are provided, there will be an accumulation of the backlash in the gear mechanisms so that there will be a time lag in an operation in the reverse direction or there will be a significant change in the operating force, depending on the angle of rotation as shown in FIG. 11.